印度-亚洲碰撞过程拉萨地块和特提斯喜马拉雅地体的运动学研究

The closure of Neo-Tethys and the continental collision between the Indian and Asian blocks have been profoundly changed the geotectonic settings of Asian continents. However, when and how the collision of India and Asia occurred have been long debated. Although a lot of new paleomagnetic data have been obtained from the Tibetan plateau in the past few years, there are still lack of consistency between these data. It is therefore difficult to be used for constraining the collision and its process between the India and Eurasia. This project is aimed to carry out a high-level studies of paleomagnetism, rock magnetism, petrography and geochronology of Cretaceous and Paleogene rocks in the east, middle and west of Lhasa block and Tethys Hymalaya Terrane, taking carefully the problem of inclination shallowing, acquired age of remanences into account. Using of apparent wander path defined by the results from different areas and/or intersection of small circles of these results, the collisional process between the India and Asia will be better rationally constrained, which will be used to reveal the characteristics of continental deformation and the mechanism of initial uplift of the Tibetan Plateau related to the India/Asia collision during the early Cenozoic. The present study has important geodynamic significance of the building of the Tibetan Plateau, and also the potential implication for understanding the inter-continental crustal deformation and process, uplift history and active tectonic evolution of the Tibetan plateau.

新特提斯洋闭合和印度-亚洲碰撞过程彻底改变了东亚的构造格局，然而，印度地块何时以何种方式拼贴到亚洲大陆之上仍未取得一致意见，尽管过去几年青藏高原获得大量的古地磁数据，但数据之间仍存在很大的差异，难以解决印亚大陆的碰撞时限和过程等，项目拟对拉萨地块和特提斯喜马拉雅地体西部、中部及东部地区的白垩纪和古近纪开展古地磁学、岩石磁学、岩相学和同位素年代学研究，加强磁倾角偏低和岩相学工作，获取具有精确的原生剩磁年代的古地磁数据，利用小圆弧交汇方法，获得地块的极移曲线，合理且精确地约束印亚碰撞过程，揭示印亚碰撞背景下欧亚大陆南缘新生代地壳构造变形特征和青藏高原隆升过程。对青藏高原地壳变形特征和过程、隆生过程和机制、时限和活动构造发展演化等重大地质问题具有重要意义。

新特提斯洋闭合和印度-亚洲碰撞过程彻底改变了东亚的构造格局，然而，印度地块何时以何种方式拼贴到亚洲大陆之上，印-亚碰撞背景下欧亚大陆南缘新生代地壳构造变形特征和青藏高原隆升过程仍不清楚，限制了对青藏高原地壳变形特征和过程、隆升过程和机制、时限和活动构造发展演化等重大地质问题的理解。.项目组对欧亚大陆南缘拉萨地块和印度地块北缘特提斯喜马拉雅地体西部、中部及东部地区分别选取合适的白垩纪和古近纪火成岩及沉积岩地层进行古地磁学、岩石磁学、岩相学和同位素年代学研究。白垩纪以来，拉萨地块西端稳定的处于19.6±0.9°N，中东部则稳定的处于10.2±0.3°N，表明在印度-欧亚板块碰撞之前，欧亚大陆南缘拉萨地块呈近北西-南东向展布。并依据特提斯喜马拉雅地体晚白垩世和古新世的古地磁结果创新性地提出了印度-亚洲碰撞的三阶段模型。但最新获得的古新世数据则说明印度板块的单阶段俯冲拼合模式，约束了印亚碰撞以来拉萨地块东部与亚洲大陆刚性块体之间发生的南北向构造缩短，约60Ma前大印度大陆与亚洲大陆南缘拉萨地块之间仍存在约2000千米的新特提斯洋，大印度的北部边缘在约50Ma时近乎同时与亚洲大陆南缘发生碰撞，随后准同步关闭赤道地区曾经存在的新特提斯洋。.通过对青藏高原内部及东南缘特提斯喜马拉雅地体、羌塘地体、保山地体、腾冲地体、兰坪-思茅地体及掸泰地体等新生代火成岩及沉积岩地层进行古地磁学、岩石磁学、岩相学和同位素年代学研究。指出东喜马拉雅构造结形成于35 Ma之后，青藏高原东南缘的地壳顺时针旋转变形启动于~27 Ma，晚于前人普遍认为的~32 Ma，青藏高原东南缘的地壳旋转变形主要受控于东喜马拉雅构造结的构造演化和北向转移，而与地壳物质的侧向挤出逃逸间的相关性较小。晚始新世之前，青藏高原的地壳增厚和隆升可能就已经弱化了青藏高原南部及其边缘的下地壳，这为青藏高原东南边缘对印度和欧亚大陆的辐合做出快速响应提供了必要条件。.在此基础上项目组开展了特提斯域内华南地块早志留纪和二叠纪峨眉山大火成岩省的古地磁研究，提出奥陶纪末-早志留纪全球真极移事件是奥陶纪末地球环境变化及生物大灭绝的根本机制，并精确限定了峨眉山玄武岩的喷发过程和持续时间。